PA radiograph

Question 1

indications of PA (12)

Answer 1

1. caries assessment
2. apical assessment
3. unerupted tooth
4. wisdom tooth
5. root morphology before extraction
6. peridontal assessment
7. root fracture
8. foreign bodies
9. teeth and alveolar bone assessment after trauma
10. during RCT
11. post op - periodontal/apical surgeries
12. post op - implant

Question 2

ideal positioning requirements of PA

Answer 2

PARRC
1. tooth and image receptor shld be parallel
2. should capture apical tissues –> incisors and canines (vertical), premolar and molars (horizontal)
3. image shld be reproducible
4. beam shld meet tooth and image receptor at right angles
5. tooth and image receptor shld be in contact

• image geometry: low OID (object to image receptor distance), use long cone to increase SID (source to image receptor distance)

Question 3

techniques of PA

Answer 3

1. Paralleling technique
   - able to meet 4/5 positioning requirements: tooth and image receptor are parallel, apical tissues captured, right angles, reproducible
   - but image receptor and tooth not in contact due anatomical restrictions
   - image geometry: use a long fsd (focal spot to skin distance) = more parallel x ray beam –> prevent magnification
2. bisecting angle
   - tooth and image receptor not parallel
   - beam is at right angles to the plane that bisects the tooth and image receptor

Question 4

advantage and disadvantage of paralleling technique

Answer 4

adv
- geometrically acurate
- holders help prod reproducible image
- no cone cut

disadv
- anatomy: flat/shallow palate, torus, shallow floor of mouth
- positioning: uncomfortable for posterior teeth, difficult to capture 3rd molar

Question 5

advantage and disadvantage of bisecting angle technique

Answer 5

adv
- fewer anatomical variations
- can be done without holder
- easier to position image receptor
- more comfortable for pt than paralleling technique

disadv
- cone cutting
- technique sensitive: vertical angulation - foreshortening or elongation/horizontal angulation - overlapping

Question 6

criteria for diagnostic radiograph for PA

Answer 6

1. appropriate density and contrast
2. 2mm beyond incisal edge and 3mm beyond apical bone
3. no overlapping proximal surface
4. no artefacts
5. incisal eges line up to edge of image receptor
6. no cone cut
7. no image distortion or blur

Question 7

common imaging errors for PA –> modifications

Answer 7

1. cone cutting
2. receptor bend- image distortion
3. horizontal angulation - proximal surface overlap
4. vertical angulation - shallow angle = elongation, steep angle = foreshortening
5. artefacts
6. blur - movement
7. bite block not at occlusal surfaces
8. double exposure - psp plate not erased properly
9. incorrect holder assembly - whole film not in hole, dot in slot